Semiconductor devices, such as transistors or the like, are the core building block of a vast majority of electronic devices. In practice, it is desirable to accurately and precisely fabricate transistors and other semiconductor devices with physical features, critical dimensions, and/or other properties of the devices having specific physical dimensions, chemistries, crystalline structures or morphologies, and/or the like to thereby achieve semiconductor devices having their intended performance characteristics and/or to improve production yield. However, the hardware tools used to fabricate such devices may exhibit performance variations. As a result, semiconductor devices may be fabricated with features that deviate from their intended structure (e.g., physically and/or chemically), which in turn can lead to performance issues and/or reduced production yield. Therefore, it is desirable to evaluate the physical features, critical dimensions, chemistries, crystalline structures or morphologies, and/or other properties of the semiconductor devices.
One technique for evaluating the properties of semiconductor devices is transmission electron microscopy (TEM) analysis. TEM is a microscopy technique in which a beam of electrons is transmitted through a thin sample, with the electrons interacting with the sample as the electrons pass through. In general, various TEM analysis techniques allow for evaluation of a target analysis area (i.e., area intended to be analyzed or otherwise evaluated) of the sample including analysis of chemical identity, crystal orientation, electronic structure, and sample induced electron phase shift as well as the regular absorption based imaging of the target analysis area. For example, the interaction of the electrons transmitted through the sample can be used to form a TEM high resolution image of the target analysis area of the sample and/or for electron energy loss spectroscopy (EELS) for chemical analysis of the target analysis area.
However, sample thickness directly affects the image resolution and signal to noise ratio of TEM analysis. As a general rule, thinner samples provide better TEM image resolution and signal-to-noise ratios than thicker samples. In many TEM analysis techniques such as atomic scale high-resolution imaging and EELS analysis, sample thicknesses below 50 nm are desirable. Some conventional approaches for preparing samples of semiconductor device structures for TEM analysis include using focused ion beam (FIB) techniques to mill a portion of the semiconductor device structure into a lamellar (e.g., thin plate form) TEM sample. Unfortunately, it is very challenging to achieve a goal of forming a lamellar TEM sample having a uniform thickness of less than about 50 nm thickness across the target analysis area using such milling techniques. In particular, typically FIB uses a focused gallium (Ga+) ion beam to mill a lamellar TEM sample to a thickness of 60 to 100 nm. However, when the lamellar TEM sample becomes thinner than, for example, about 60 nm, it is challenging to continue milling the sample due to uneven stresses that develop in the sample and that can cause the sample to bend. Sample bending during milling can result in an uneven milling rate across the sample that can damage and prevent accurate evaluation of the target analysis area.
Accordingly, it is desirable to provide methods for evaluating semiconductor device structures including forming an ultra-thin lamellar sample portion of the semiconductor device structure having a relatively uniform thickness across its target analysis area for evaluation using, for example, a transmission electron microscopy (TEM) arrangement. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.